Joint diseases resulting from osteoarthritis and other diseases which trigger the destruction of cartilage are causes of economic and social loss, and can be considered as major health problems (1, 2).
Osteoarthritis results from the degradation of articular cartilage. It is estimated that up to 60% of the population aged over 75 years old suffer from this disease (3). The real cause of osteoarthritis is still unknown but some reports mention that while this disease is developing cartilage, subchondral bone and synovial membrane undergo some changes. The pathogenesis of this disease causes the affected cartilage to lose resistance to outer impact and also the elasticity and smoothness of the joint.
While rheumatoid arthritis is a progressive destruction of the cartilage similar to osteoarthritis (OA), patients suffering from rheumatoid arthritis (RA) experience the tearing and destruction of macromolecules which are major components of cartilage by proteolytic cleavage; the degradation products are then released to the synovial fluid. The degradation of the surface of articular cartilage and cartilage thickness can be assessed by x-ray diagnosis of the affected joints, but this will only be apparent after a long period of these diseases, which can often be too late for treatment (4, 5).
Provision of an alternative diagnostic test for arthritis and/or other cartilage degradation would therefore be beneficial to patients. In particular, detection of cartilage degradation products in synovial fluid would assist in the development of diagnostic tests which allow diagnosis at an early stage. Such a test may also assist in monitoring the disease and as a prognosis marker at the different stage of the diseases.
There is an existing test for diagnosis of degenerative joint diseases (6). Quantitation of proteoglycans and their fragments, especially glycosaminoglycans, can be done by an immunoassay using specific monoclonal antibodies to the proteoglycan fragments and other biochemical markers in the cartilage. Monoclonal antibodies have been produced against proteoglycan fragments such as anti-keratan sulfate peptides (KS-peptides) (7), chondroitin sulfate epitopes (CS-epitope) (8, 9), and hyaluronan (HA) (10). Using these antibodies and binding proteins in immunoassays, especially, ELISA-based techniques, can allow a quantitative test of these biomolecules to be performed.
Furthermore, certain types of cancer are known to over-produce these and related biomolecules. Furthermore, cancers can produce many enzymes that degrade biomolecules in connective tissues surrounding them. So, proteoglycans containing chondroitin sulfate can be a useful marker indicating the existence of cancers and can be a potential marker for a prognosis or treatment of disease activities.